Flex-rigid wiring board and method of manufacturing the same

ABSTRACT

A flex-rigid wiring board includes a flexible board including a flexible substrate and a conductor pattern formed over the flexible substrate, a non-flexible substrate disposed adjacent to the flexible board, an insulating layer covering the flexible board and the non-flexible substrate and exposing one or more portions of the flexible board, a conductor pattern formed on the insulating layer, and a plating layer connecting the conductor pattern of the flexible board and the conductor pattern on the insulating layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of and claims the benefits ofpriority to U.S. application Ser. No. 11/876,413, filed Oct. 22, 2007,which claims the benefits of priority to U.S. application No.60/853,423, filed Oct. 23, 2006. The contents of these applications areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wiring board including a flexibleportion and a method of manufacturing the same.

2. Discussion of the Background

Flex-rigid wiring boards each including a rigid portion and a flexibleportion are described in, for example, Japanese Unexamined PatentApplication Publication Nos. 2006-140213 and 2006-100703, andInternational Publication No. WO2004/093508.

A flex-rigid wiring board described in Japanese Unexamined PatentApplication Publication No. 2006-140213 includes a core board providedas a rigid portion, a flexible board disposed adjacent to the core boardin the horizontal direction, a flexible adhesive layer laminated on thecore board and the flexible board, a wiring pattern formed on theflexible adhesive layer disposed in the rigid portion, and blind viasand/or through holes for connecting wiring patterns formed in respectivelayers. In this constitution, the flexible adhesive layer is laminatedon the flexible board.

Japanese Unexamined Patent Application Publication No. 2006-100703describes a method of manufacturing a flex-rigid wiring board. In themethod, first, a rigid board having a vertical wiring portion formed ina connection region thereof and a flexible board having a connectionterminal formed at an end thereof are separately formed. Then, theconnection region of the rigid board is cut out to a depth larger thanthe thickness of the flexible board to form a step. Next, the connectionterminal of the flexible board is connected to the vertical wiringportion of the step.

A flex-rigid wiring board disclosed in WO2004/093508 includes a rigidboard and a flexible board which are bonded together with an insulatingadhesive to form a unified body. Furthermore, connection electrode padsof the rigid board and the flexible board are electrically andphysically connected through bulk conductors provided through theinsulating adhesive. In the flex-rigid wiring board with theabove-described constitution, the flexible board is disposed on one ofthe sides of the rigid substrate, and laser is applied to the flexibleboard side to form vias for plating connection.

The contents of the above mentioned publications are incorporated hereinby reference in their entirety.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a flex-rigid wiringboard includes a flexible board including a flexible substrate and aconductor pattern formed over the flexible substrate, a non-flexiblesubstrate disposed adjacent to the flexible board, an insulating layercovering the flexible board and the non-flexible substrate and exposingone or more portions of the flexible board, a conductor pattern formedon the insulating layer, and a plating layer connecting the conductorpattern of the flexible board and the conductor pattern on theinsulating layer.

According to another aspect of the present invention, a flex-rigidwiring board includes a flexible board including a flexible substrateand a conductor pattern formed over the flexible substrate, anon-flexible substrate disposed adjacent to the flexible board, aninsulating layer covering the flexible board and the non-flexiblesubstrate and exposing one or more portions of the flexible board, aconductor pattern formed on the insulating layer, and a via formed inthe insulating layer and connecting the conductor pattern on theinsulating layer and the conductor pattern of the flexible board.

According to yet another aspect of the present invention, a flex-rigidwiring board includes a flexible board including a flexible substrateand a conductor pattern formed over the flexible substrate, anon-flexible substrate disposed adjacent to the flexible board, aninsulating layer covering the flexible board and the non-flexiblesubstrate and exposing one or more portions of the flexible board, aconductor pattern formed on the insulating layer, and a via formed inthe insulating layer and connecting the conductor pattern on theinsulating layer and the conductor pattern of the flexible board. Theflexible board further includes a protective layer covering theconductor pattern of the flexible board, and the via formed in theinsulating layer includes a plating layer.

According to still another aspect of the present invention, a method ofmanufacturing a flex-rigid wiring board includes disposing a flexibleboard including a flexible substrate and a conductor pattern formed overthe flexible substrate and a non-flexible substrate adjacent to eachother, covering a boundary between the flexible board and thenon-flexible substrate with an insulating layer, providing a conductorpattern on the insulating layer, forming a via hole opening which passesthrough the insulating layer and reaches the conductor pattern of theflexible board, and plating the via hole opening to form a viaconnecting the conductor pattern of the flexible board and the conductorpattern on the insulating layer.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIGS. 1A and 1B are a side view and a plan view of a flex-rigid wiringboard according to an embodiment of the present invention;

FIG. 2 is a partially enlarged view of FIG. 1A;

FIG. 3 is a view showing a modified example of the flex-rigid wiringboard shown in FIG. 2;

FIG. 4 is a side view of a flexible board;

FIGS. 5A to 5L are views illustrating steps of a method of manufacturinga flex-rigid wiring board according to an embodiment of the invention;

FIGS. 5A′, 5G′, 5K′ and 5L′ are views illustrating modified steps of themethod of manufacturing a flex-rigid wiring board shown in FIGS. 5A to5L;

FIGS. 5F″, 5G″ 5K″ and 5L″ are views illustrating other modified stepsof the method of manufacturing a flex-rigid wiring board shown in FIGS.5A to 5L;

FIGS. 6A to 6F are enlarged views illustrating the method ofmanufacturing a flex-rigid wiring board shown in FIGS. 5A to 5L;

FIG. 7 is a view showing a modified example of the flex-rigid wiringboard shown in FIG. 2;

FIG. 8 is another view showing a modified example of the flex-rigidwiring board shown in FIG. 2;

FIG. 9 is a view showing an example of fan-out of a wiring pattern;

FIG. 10 is a view showing an example in which a flexible substrate ispartially widened to increase strength; and

FIG. 11 is another view showing an example in which a flexible substrateis partially widened to increase strength.

DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings.

A flex-rigid wiring board 10 according to an embodiment of the presentinvention will be described.

As shown in FIGS. 1A and 1B, the flex-rigid wiring board 10 according tothis embodiment includes a first rigid board (rigid board) 11, a secondrigid board 12, and a flexible board 13 connecting the rigid boards 11,12 to each other.

On each of the first and second rigid boards 11, 12, any desired circuitpattern is formed. For example, an electronic component such as asemiconductor chip may be connected to each board.

On the flexible board 13, stripe-shaped wiring (13 a) is formed forconnecting the circuit patterns on the first and second rigid boards 11,12. The wiring (13 a) connects the circuit patterns on the rigid boards11, 12 to each other.

Next, with respect to the structure of the junction portions between therigid boards 11, 12 and the flexible board 13, the junction portionbetween the rigid board 11 and the flexible board 13 will be describedreferring to an example as shown in FIG. 2. FIG. 2 is an enlargedsectional view of an area denoted by reference numeral 2 in FIG. 1A.

As shown in the drawing, the flexible board 13 has a structure in whicha substrate 131, conductor layers 132, 133, insulating films 134, 135,shield layers 136, 137, and cover lays 138, 139 are laminated. One ormore of the insulating films 134, 135, shield layers 136, 137, and coverlays 138, 139 may constitute a protective layer.

The substrate 131 is composed of an insulating flexible sheet, forexample, a polyimide sheet having a thickness of 20 to 50 μm, preferablyabout 30 μm.

The conductor layers 132, 133 are formed on the front and back surfacesof the substrate 131, respectively, and each have a wiring stripepattern (13 a). For example, each of the conductor layers 132, 133 has acopper pattern having a thickness of about 5 to 15 μm.

The insulating films 134, 135 may be composed of a polyimide film havinga thickness of about 5 to 15 μm and insulate the conductor layers 132,133, respectively, from the outside.

The shield layers 136, 137 (also referred as electromagnetic shieldlayers) may be conductive layers each including a silver paste curedfilm and shield the conductor layers 132, 133 from externalelectromagnetic noise and shield the emission of electromagnetic noisetoward the outside.

The cover lays 138, 139 include insulating films of polyimide or thelike having a thickness of about 5 to 15 μm and insulate and protect thewhole flexible board 13 from the outside.

On the other hand, the rigid board 11 includes a laminate of a firstinsulating layer 111, a non-flexible substrate 112, a second insulatinglayer 113, and first and second upper insulating layers 114, 115.

The non-flexible substrate 112 gives rigidity to the rigid board 11 andis composed of a non-flexible insulating material such as a glass epoxyresin. The non-flexible substrate 112 is disposed with a space from theflexible board 13 in a horizontal direction. The non-flexible substrate112 has substantially the same thickness as the flexible board 13, forexample, 50 to 150 μm, preferably about 100 μm.

Each of the first and second insulating layers 111, 113 may be formed bycuring prepreg, for example, glass clothes (111 a, 113 a) impregnatedwith resin 125, and has a thickness of 50 to 100 μm, preferably about 50μm.

The prepreg preferably contains a resin having a low flowcharacteristic. Such prepreg can be prepared by impregnating a glasscloth with an epoxy resin and then thermally curing the resin tofacilitate the progress of curing in advance.

The prepreg can also be formed by impregnating a glass cloth with aresin with high viscosity, impregnating a glass cloth with a resincontaining an inorganic filler, e.g., a silica filler, or impregnating aglass cloth with a decreased amount of resin.

The first and second insulating layers 111, 113 cover both the front andthe back surfaces of the non-flexible substrate 112 and the flexibleboard 13 to partially expose the flexible board 13. The resin of thefirst and second insulating layers 111, 113 is overlapped with the resinof the cover lays 138, 139 on the surfaces of the flexible board 13.

The non-flexible substrate 112 and the first and second insulatinglayers 111, 113 constitute the core of the rigid board 11 to support therigid board 11 and hold one of the ends of the flexible board 13 tosupport and fix the flexible board 13.

The spaces formed by the non-flexible substrate 112, the flexible board13, and the first and second insulating layers 111, 113 are filled witha resin 125. The resin 125 seeps from the low-flow prepreg constitutingthe first and second insulating layer 111, 113, for example, duringmanufacture. The resin 125 is cured integrally with the first and secondinsulating layers 111, 113.

Furthermore, in the second insulating layer 113, via openings (via holeor contact hole) 116 are formed in a portion opposing connection pads(13 b) of the wiring 133 of the flexible board 13.

In the flexible board 13, the shield layer 137 and the cover lay 139 ofthe flexible board 13 are removed from a portion opposing the vias 116(a portion in which the connection pads (13 b) of the conductor layer(13 a) are formed). The via openings 116 pass through the insulatingfilm 135 of the flexible board 13 to expose the connection pads (13 b)of the conductor layer 133.

In addition, a conductor layer 117 (may also be referred as vias, viahole conductor structure, or via contact) is formed on the inner surfaceof each of the via openings 116 by copper plating or the like. Theconductor layers or vias 117 are connected to the connection pads (13 b)of the conductor layer 113 of the flexible board 13 by plating. The viaopenings 116 are filled with a resin.

Furthermore, an extraction pattern 118 is formed on the secondinsulating layer 113 to be connected to the conductor layers or vias117. The extraction pattern 118 includes a copper plating layer.

Furthermore, a copper pattern 124 insulated from other components isformed at an end of the second insulating layer 113, i.e., at a positionbeyond the boundary between the flexible board 13 and the non-flexiblesubstrate 112. Therefore, heat generated in the rigid board 11 iseffectively radiated.

The first upper insulating layer 114 is laminated on the secondinsulating layer 113. The first upper insulating layer 114 may be formedby curing a material containing an inorganic material, for example,prepreg prepared by impregnating a glass cloth with a resin. Thisimproves the resistance to dropping impact.

In the process of manufacturing the flex-rigid wiring board, the viaopenings 116 are filled with the resin seeping from the prepreg.

Furthermore, the second upper insulating layer 115 is disposed on thefirst upper insulating layer 114. The second upper insulating layer 115may also be formed by curing prepreg including a glass cloth impregnatedwith a resin.

In the first upper insulating layer 114 disposed on the secondinsulating layer 113, via openings (first upper via openings) 119 areformed and connected to the extraction pattern 118. The via openings 119are filled with a conductor 120 (may also be referred as upper vias,upper via hole conductor structure, or upper via contact) such as copperor the like. In the second upper insulating layer 115 laminated on thefirst upper insulating layer 114, via openings (second upper viaopenings) 121 are formed and connected to the via openings 119. The viaopenings 121 are filled with a conductor 122 (also referred as vias, viahole conductor structure, or via contact) such as copper or the like.Namely, the vias 120, 122 (may also be referred as upper vias) formfilled built-up vias.

Furthermore, a conductor pattern (circuit pattern) 123 is appropriatelyformed on the second upper insulating layer 115. The vias 120 areappropriately connected to the conductor pattern 123.

The constitution of the connection portion between the rigid board 12and the flexible board 13 is similar to that of the connection portionbetween the rigid board 11 and the flexible board 13.

In the flex-rigid wiring board 10 having the above constitution, the endof the flexible board 13 is held between the first and second insulatinglayers 111, 113 which constitute the core portion of the rigid board 11and subjected to resin polymerization.

Furthermore, the connection pads (13 b) of the conductor layer 133 ofthe flexible board 13 are connected to the conductor pattern 123 of therigid board 11 through the vias or copper plating layers 117 formed inthe via openings 116 which are formed in the second insulating layer 113and the insulating film 135.

Therefore, when the flexible board 13 is bent, stress applied to theflexible board 13 is not transmitted to the connection portion (the viaopenings 116 and the vias 117) of the rigid board 11. Thus, stressapplied to the connection portion between the rigid board 11 and theflexible board 13 is decreased and reliability is improved.

The conductor layer 133 of the flexible board 13 is connected by platingto the vias 117 in the via openings 116 of the rigid board 11.Therefore, the connection portion has high reliability.

The via openings 116 are filled with the resin of the upper insulatinglayer 114. Since the vias 117 are fixed and supported by the resin inthe via openings 116, the connection reliability between the vias 117and the conductor layer 133 is improved.

The end surfaces of the insulating layers 113, 111 which face theflexible board 13 project beyond the end of the upper insulating layer114 which faces the flexible board 13. Therefore, when the flexibleboard 13 is bent, stress applied to the flexible board 13 is nottransmitted to the connection portion (the via openings 116 and the vias117) of the rigid board 11. Thus, stress applied to the connectionportion between the rigid board 11 and the flexible board 13 isdecreased and reliability is improved.

The horizontal extension and contraction of the extensible flexibleboard 13 is suppressed by the core portion of the rigid board 11.Therefore, bending reliability and heat resistance reliability are high.Also, the flexible substrate portion of the flexible board 13 is exposedbetween the rigid boards 11, 12, and thus bending stress applied towiring is small as compared with a case in which the whole is coveredwith an insulating resin or the like.

In the flex-rigid wiring board 10, an end portion of the flexible board13 is held between the first and second insulating layers 111, 113 ofthe rigid board 11. Therefore, a change in dimensions of the flexibleboard 13 has small influence, and a positional error of the connectionlands (the vias 117) of the rigid board 11 is deceased. Thus, the viaopenings 116 having a smaller diameter may be designed.

The flexible board 13 is not disposed in the rigid boards 11, 12.Therefore, a degree of reliability similar to that of a conventionalrigid board is maintained. In addition, there is high resistance to aplating solution and a general-purpose plating solution may be used.Similarly, since a flex material is not used in a rigid portion, thesame heat resistance as a usual rigid portion can be maintained.

Furthermore, the flexible board 13 is partially used and effectivelydisposed, thereby suppressing the manufacturing cost.

Each of the upper insulating layers 114, 115 may be formed from usualprepreg. Usual prepreg is excellent in compatibility between inner layerpatterns, and thus insulation deterioration due to the occurrence ofvoids or the like is avoided. In addition, a fine pattern, for example,a pattern with L/S of 60/50 or 50/50 μm, is realized. This can beachieved with a limitation on material control.

Furthermore, a general-purpose interlayer material (prepreg) may be usedas each of the upper insulating layers 114, 115. Therefore, in themanufacturing process, IVH (Interstitial Via Hole) including the viaopenings 116 is filled with the resin constituting the upper insulatinglayers 114, 115. Thus, a resin exclusively used for filling in holesneed not be used.

When a glass epoxy substrate is used as the core portion of each of therigid boards 11, 12, dropping impact resistance is improved.

In this embodiment, a conductor pattern is formed only on the uppersurface of each of the rigid boards 11, 12 for easier understanding.However, the present invention is not limited to such an example. Forexample, as shown in FIG. 3, a conductor pattern may be formed on thelower surface of each of the rigid boards 11, 12.

In the constitution shown in FIG. 3, vias 141 are formed in the firstinsulating layer 111 and the insulating film 134 of the flexible board13. In each via 141, a conductor pattern 142 is formed and connected toan extraction pattern 143 formed on the first insulating layer 111. Theconductor pattern 142 and the extraction pattern 143 are formed bypatterning a copper plating layer.

Furthermore, third and fourth upper insulating layers 144, 145 arelaminated on the first insulating layer 111. Via openings 146, 147 areformed in the third and fourth upper insulating layers 144, 145,respectively. The via openings 146, 147 are filled with conductors 148,149 (also referred as vias, via hole conductor structure, or viacontact), respectively. A conductor pattern 150 is formed on the prepreg145.

Next, according to one embodiment of the present invention, a method ofmanufacturing the flex-rigid wiring board 10 having the above-descriedconstruction is described.

First, a method for manufacturing the flexible board 13 will bedescribed.

Copper films are formed on both surfaces of the polyimide substrate 131processed into a predetermined size. Next, the copper films arepatterned to form the conductor layers 132, 133 each having the wiringpattern (13 a) and the connection pads (13 b).

The insulating films 134, 135 each including a polyimide layer areformed on the polyimide substrate 131 and the conductor layers 132, 133,respectively. Furthermore, silver paste is applied except on the end ofthe flexible board 13, and the applied silver paste is cured to form theshield layers 136, 137.

Then, the cover lays 138, 139 are formed to cover the shield layers 136,137 on the front and the back surfaces, respectively.

As a result, the flexible board 13 having the constitution shown in FIG.4 is completed. The shield layers 136, 137 and the cover lays 138, 139are formed avoiding the connection pads (13 b).

Next, a method of bonding the rigid boards 11, 12 and the flexible board13 together is described.

First, as shown in FIG. 5A, the first insulating layer 111, thenon-flexible substrate 112, and the second insulating layer 113, whichconstitute the core of the rigid board 11, are aligned. Each of thefirst and second insulating layers 111, 113 includes, for example, aprepreg having a thickness of 20 to 50 μm, and the non-flexiblesubstrate 112 includes, for example, a glass epoxy substrate having athickness of about 100 μm.

As shown in FIG. 2, the thickness of the non-flexible substrate 112 ispreferably substantially the same as the thickness of the flexible board13. In such a structure, the space between the non-flexible substrate112 and the cover lay 139 is filled with the resin 125, and thus theflexible board 13 and the non-flexible substrate 112 are securely bondedtogether.

The resin 125 filled in the space is cured integrally with theinsulating layer 113 to fix the peripheries of the vias 117 with theresin 125, thereby improving the reliability of connection between thevias 117 and the conductor layer 133.

Similarly, the non-flexible substrate and the first and secondinsulating layers constituting the core of the rigid board 12 arealigned.

Furthermore, one of the ends of the flexible board 13 is insertedbetween the first and second insulating layers 111, 113 of the rigidboard 11 and aligned, and the other end is disposed between the firstand second insulating layers and the non-flexible substrate of the rigidboard 12. Furthermore, conductor films 161, 162 (also referred as“copper foils”) are disposed on and below these layers. A separator maybe provided on the flexible board 13 before conductor films 161,162 isdisposed on and below these layers.

Next, as shown in FIG. 5B, these layers are pressed under pressure. Atthis time, as shown in an enlarged view of FIG. 6A, the spaces betweenthe non-flexible substrate 112 and the flexible board 13 are filled withthe resin 125 extruded from the prepreg constituting the first andsecond insulating layers 111, 113. Since the spaces are filled with theresin 125, the flexible board 13 and the non-flexible substrate 112 aresecurely bonded together.

The pressure pressing is performed, for example, using a hydropressapparatus at a temperature of 200° C. and a pressure of 40 kgf for apressure time of about 3 hours.

Then, the whole is heated to cure the prepreg constituting the first andsecond insulating layers 111, 113 and the resin 125 and integrated. Atthe same time, the resin of the cover lays 138, 139 of the flexibleboard 13 and the resin of the first and second insulating layers 111,113 are overlapped. The resin of the insulating layers 111, 113 isoverlapped and fixes the peripheries of the vias 117, thereby improvingthe reliability of connection between the via 117 and the conductorlayer 133.

Next, as shown in FIG. 5C, IVH (Interstitial Via Hole) 163 is formed,for example, by irradiation of CO₂ laser from a CO₂ laser processingapparatus accordingly. At the same time, as shown in an enlarged view ofFIG. 6B, the via openings 116, 141 are formed for connecting the wiringlayers 132, 133 of the flexible board 13 to the rigid boards 11, 12.

Then, as shown in FIG. 5D, copper plating is conducted on the surfacesof the whole structure. The copper plating layers and the copperpatterns 161, 162 previously formed are integrated to form a copper film171 over the entire surface of the board. As shown in FIG. 6C, thecopper plating layer 117 is formed in the vias openings 116, 141. In thecopper plating, the flexible board 13 is covered with the copper foils161, 162 and does not make direct contact with a plating solution.Therefore, the flexible board 13 is not damaged by the plating solution.

Then, as shown in FIG. 5E, the copper film 171 on the surface of theboard is patterned. In this step, the vias 117, 142 connected to theconductor layers 132, 133 of the flexible board 13 and the extractionpatterns 118, 143 are formed. At the same time, as shown in FIG. 6D, thecopper film 171 is left on the end portions of the first and secondinsulating layers 111, 113.

Then, as shown in FIG. 5F, the first and third upper insulating layers114, 144 are disposed on and below the resulting structure. Each of thefirst and third upper insulating layers 114, 144 includes, for example,a prepreg prepared by impregnating a glass cloth with a resin. The viaopenings 116, 141 are filled with the resin from the prepreg.

Then, the resin in the prepreg and the vias is cured by heating tosolidify the first and third upper insulating layers 114, 144. Next, thevia openings 119, 146 are formed in the first and third upper insulatinglayers 114, 144, respectively, and filled with a conductor by copperplating or the like. The via openings 119, 146 may be filled withconductive paste (e.g., thermosetting resin containing conductiveparticles) by printing such as screen printing and then subjected toresin curing.

Then, as shown in FIG. 5G, the second and fourth upper insulating layers115, 145 are disposed on and below the whole board. Each of the secondand fourth upper insulating layers 115, 145 includes, for example, usualprepreg prepared by impregnating a glass cloth with a resin. Before thesecond and fourth upper insulating layers 115,145 are formed, aseparator may be disposed in an opening formed in the first and thirdupper insulating layers 114, 144.

Next, the resin of the prepreg is cured by heating to solidify thesecond and fourth upper insulating layers 115, 145.

Furthermore, the via openings 121, 147 are formed in the second andfourth upper insulating layers 115, 145, respectively, and filled with aconductor by copper plating. The via openings 121, 147 may be filledwith conductive paste (e.g., thermosetting resin containing conductiveparticles) by printing such as screen printing and then subjected toresin curing. When the via openings 121, 147 are filled with the sameconductive paste material, connection reliability of the vias 122, 149(also referred as upper vias) against the thermal stress is improved.

If required, as shown in FIG. 5H, copper foil sheets with resin (resincopper film: RCF) 172, 173 are disposed on the outermost layers of theboard and pressed.

Then, the whole structure is heated to cure the resin.

Next, as shown in FIG. 5I, via openings 174, 175 are formed in the RCFs172, 173, respectively. Next, the via openings 174, 175 are filled witha conductor by copper plating. If required, the surface copper foils arepatterned to form conductor patterns.

Next, as shown in FIGS. 5J and 6E, the joint portions between the rigidboards 11, 12 and the flexible board 13 are irradiated with laser beam158, for example, CO₂ laser, using as a stopper the copper foil 171formed at the ends of the cores of rigid boards 11, 12 to cut the upperinsulating layers 114, 115, 144, 145, and the copper foil sheets withresin (RCFs) 172, 173. In this step, the energy or irradiation time iscontrolled such that the copper foil 171 used as a stopper is cut tosome extent.

As a result, as shown in FIG. 5H, a structure 181 on the flexible board13 is separated from the other portions.

Then, as shown in FIG. 5L, the structure 181 is removed from theflexible board 13 by peeling. The copper foils 161, 162 (refer to FIG.5B), which are a base of the remaining copper foil 171, are only pressedby the cover lays 138, 139 of the flexible board 13 and are not fixed.Similarly, the copper foil 171 is not fixed to the flexible board 13.Therefore, the copper foil 171 is also removed by removal of thestructure 181.

Consequently, portions of the copper foil 171 not covered with the othercomponents are removed. Therefore, the copper foils 124, 151 are left onportions covered with the prepregs 113, 144 at the ends of the first andsecond insulating layers 111, 113.

As a result, the flex-rigid wiring board 10, in which the ends of theflexible board 13 are held between the core portions (the first andsecond insulating layers 111, 113) of the rigid boards 11, 12, and thelands of the rigid boards 11, 12 are connected to the connection pads ofthe flexible board by plating, is completed.

In the above-described structure, plating on the polyimide of theflexible board 13 is not required, thereby securing connectionreliability.

In addition, RCF can be used on the outermost layers of the rigid boards11, 12. Therefore, similar reliability and dropping resistance as thoseof a conventional rigid board are secured.

In the manufacturing method, prepreg including a resin having a low flowproperty is used for forming the core layer of each of the rigid boards11, 13. However, usual prepreg may be used for layers other than thecore layers, and thus IVH filling is not required, and voids are seldomformed.

Furthermore, only a bending portion includes a flexible board, and thusstability is improved.

Furthermore, holes are formed in multiple layers by laser processingafter the formation of outer layers, and thus the manufacturing cost canbe suppressed.

Since holes are formed in multiple layers by laser processing after theformation of outer layers, opening accuracy of the flexible board isincreased.

Since a glass epoxy substrate is used for the core portions of the rigidboards 11, 12, dropping impact resistance is improved.

A method for manufacturing the flex-rigid wiring board 10 is not limitedto those steps referred in FIGS. 5A to 6L. For example, referring toFIG. 5A′, a separator 291 may be provided in a gap (113 a) formed in thesecond insulating layer 113. The separator 291 may be, for example, acured prepreg or a polyimide film. Also, an adhesive may be providedbetween the separator 291 and the copper film 171. In such a case,through the steps shown in FIGS. 5B to 5F, the copper film 171 and theupper insulating layers 114, 115 may be formed over the separator 291 asshown in FIG. 5G′. Subsequently, through the steps shown in FIGS. 5H to5I, the copper film sheet with resin (Resin Copper Film or RCF) 173 isprovided over the upper insulating layer 115, and the via opening 174 isformed and filled with conductive material. Then, the boundary betweenthe upper insulating layer 113 and the separator 291 is cut by the laserbeam 158, using the copper film 171 as a stopper. At this time, theenergy or irradiation time of the laser beam 158 may be adjusted suchthat the copper film 171 is cut appropriately to some extent. As such, astructure 181 over the flexible board 13 is separated as shown in FIG.5K′. Then, the structure 181 may be torn off and removed from theflexible board 13 as shown in FIG. 5L′. The separator 291 makes easierto tear off and remove the structure 181 from the flexible board 13.Also, the separator 291 supports the copper film 171 and prevents aplating solution from seeping into the gap (113 a) between the flexibleboard 13 and the copper film 162 and the copper film 171 from beingtorn.

Also, referring to FIGS. 5F″, 5G″, 5K″ and 5L″, another method formanufacturing the flex-rigid wiring board 10 is described below as amodification from the steps shown in FIGS. 5A to 6L. In thismodification, after the separator 291 is provided, the steps describedin FIGS. 5B through 5F are carried out. Then, using a laser, a cut line292 may be formed in a portion of the upper insulating layer 114 abovethe separator 291 as shown in FIG. 5F″. Thereafter, the upper insulatinglayer 115 is provided over the upper insulating layer 114. However, inthe place of a portion of the upper insulating layer 115, a separator293 having one edge portion reaching over the cut line 292 is providedas shown in FIG. 5G″. Subsequently, the resin bearing copper film sheet173 is provided over the upper insulating layer and the separator 293 bycarrying out the steps described in FIGS. 5H and 5I, a via opening isformed in the upper insulating layer 115, and copper plating isconducted. Then, using a laser, cut lines 294, 295 are formed over oneedge portion of the separator 291 and over the other edge portion of theseparator 293 as shown in FIG. 5K″. Finally, as shown in FIG. 5L″, astructure 296 defined by the cut line 294, the separator 291, the cutline 292, the separator 293 and the cut line 295 is removed. With such astructure, a portion or portions which do not contribute to theformation of circuitry may be removed and the volume of a wiring boardmay be reduced.

In the above, the modifications concerning the manufacturing stepsrelated to the rigid board 12 are described. However, such modificationsmay be applied to the manufacturing steps of the rigid board 11 or bothof the rigid boards 11, 12. Also, in the examples described above, themodifications describe the manufacturing steps concerning the upperportions of the flex-rigid wiring board 10. However, such modificationsmay be applied to the lower portions of the flex-rigid wiring board 10or the flex-rigid wiring board 10 as a whole.

Although the flex-rigid wiring board 10 according to an embodiment ofthe present invention is descried above, the present invention is notlimited to this embodiment. For example, the materials, sizes, andnumber of the layers may be appropriately changed.

As illustrated in FIG. 7, the via openings 116, 141 may be filled with aconductor such as a plating metal. When the via openings 116, 141 arenot completely filled with the resin, voids are formed in the viaopenings 116, 141. In this case, when heat is applied to the flex-rigidwiring board 10, the connection reliability of the vias may becompromised due to the expansion of the voids. When the via openings116, 141 are filled with a plating metal as shown in FIG. 7, theconnection reliability of the vias 117, 142 against the heat can beimproved.

Similarly, conductor patterns (circuit patterns) 191, 192 may be formedon the non-flexible substrate 112, for connection with any desiredportion.

Also, conductor patterns (circuit patterns) 193, 194 may be formed onthe first and third upper insulating layers 114, 144, for connectionwith any desired portion.

The conductor patterns 191, 143, 193, 150 are connected to each otherthrough the vias 148, 149 and other vias. Similarly, the conductorpatterns 192, 118, 194, 123 are connected to each other through the vias120, 122 and other vias. Furthermore, the conductor patterns 123, 150are connected to each other through the vias formed in the via openings163.

The first and second insulating layers 111, 113 which hold the end ofthe flexible board 13 therebetween may be composed of RCF. Each of thefirst and third upper insulating layers 114, 144 and the second andfourth upper insulating layers 115, 145 may be composed of RCF. In thisconstitution, a manufacturing step can be omitted.

Although, in this embodiment, the flexible board 13 and the non-flexiblesubstrate 112 have substantially the same thickness, the presentinvention is not limited to such an example. For example, as shown inFIG. 8, the flexible board 13 may be thinner than the non-flexiblesubstrate 112. In this case, the spaces between the flexible board 13,the non-flexible substrate 112, and the first and second insulatinglayers 111, 113 are filled with a resin, for example, the resin seepingfrom the insulating layers 111, 113 or a resin previously inserted foradjusting the height during manufacture. In this way, the spaces arefilled with the resin 125, and thus the flexible board 13 and thenon-flexible substrate 112 are securely bonded together.

The resin is integrally cured and solidified by heating duringmanufacture. Since the resins of the insulating layers 111, 113 areoverlapped, and the resin 125 is integrally cured and solidified, theperipheries of the vias 117, 142 are fixed with the resin and thereliability of connection between the vias 117, 142 and the conductorlayers 133, 132 is improved.

In addition, the wiring patterns formed on the rigid boards 11, 12 andthe flexible board 13 are not limited to the example shown in FIG. 1.For example, as illustrated in FIG. 9, the wiring patterns may be formedin a shape which fans out from the flexible board 13 toward the rigidboards 11, 12. Namely, the pitch of the connection portion (13 b) may bemade larger than that of wiring (13 a) of the flexible board 13. In thiscase, more wirings are disposed on the flexible board 13, and thus aflex-rigid wiring board having high-density wiring may be formed.

In order to increase the strength of the boundary portions between therigid boards 11, 12 and the flexible board 13, as illustrated in FIGS.10 and 11, the flexible board 13 may be partially widened. In this case,the area of connection between the flexible board 13 and the rigidboards 11, 12 is increased, thereby improving the connection reliabilityof vias.

For example, in an example shown in FIG. 10, an end of the flexibleboard 13 is widened to increase the area of a portion to be fixed toeach of the rigid boards 11, 12. In this case, the strength of the endsof the flexible board 13 is increased and bending resistance isimproved.

In an example shown in FIG. 11, projections are formed at a positionwhere bending of the flexible board 13 is to be repeated (for example,the position corresponding to the end surfaces of the rigid boards 11,12) to increase the strength of the position where bending is repeated.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A method of manufacturing a flex-rigid wiring board, comprising:disposing a flexible board comprising a flexible substrate and aconductor pattern formed over the flexible substrate and a non-flexiblesubstrate adjacent to each other; covering a boundary between theflexible board and the non-flexible substrate with an insulating layer;providing a conductor pattern on the insulating layer; forming a viahole opening which passes through the insulating layer and reaches theconductor pattern of the flexible board; and plating the via holeopening to form a via connecting the conductor pattern of the flexibleboard and the conductor pattern on the insulating layer.
 2. The methodaccording to claim 1, further comprising: filling a space formed by thenonflexible substrate, the flexible substrate, and the insulating layerwith a resin; and curing the resin filled in the space integrally withthe insulating layer comprising the resin.
 3. The method according toclaim 1, wherein the plating further comprises filling the via with aplating metal.
 4. The method according to claim 1, wherein the coveringcomprises forming the insulating layer covering a front surface and aback surface of the boundary between the flexible substrate and thenon-flexible substrate.
 5. The method according to claim 1, furthercomprising: disposing a metal foil over the insulating layer and theflexible substrate; disposing a second insulating layer over the metalfoil; and cutting the second insulating layer at a positioncorresponding to an end portion of the insulating layer by laser usingthe metal foil as a stopper.
 6. The method according to claim 1, furthercomprising: disposing a metal foil over the insulating layer and theflexible substrate; disposing a second insulating layer over the metalfoil; cutting the second insulating layer at a position corresponding toan end portion of the insulating layer by laser using the metal foil asa stopper; and removing a portion of the metal foil and a structureremaining on the flexible substrate after the cutting.
 7. The methodaccording to claim 1, further comprising: disposing a metal foil overthe insulating layer and the flexible substrate; patterning the metalfoil to form a circuit pattern over the insulating layer; disposing asecond insulating layer over the metal foil; and cutting the secondinsulating layer by laser at a position corresponding to an end portionof the insulating layer using the metal foil as a stopper.
 8. The methodaccording to claim 1, further comprising: disposing a metal foil overthe insulating layer and the flexible substrate; disposing a secondinsulating layer over the metal foil; forming a conductor pattern overthe second insulating layer; and cutting the second insulating layer bylaser at a position corresponding to an end portion of the insulatinglayer using the metal foil as a stopper.
 9. The method according toclaim 1, further comprising filling the via with a resin included in thesecond insulating layer.
 10. The method according to claim 1, whereinthe covering comprises forming the insulating layer comprising a glasscloth and a resin.